Physiological measurement system with automatic wavelength adjustment

ABSTRACT

Disclosed herein is a physiological measurement system that can automatically adjust the number of wavelengths used based on the quality of a sensor signal that is reflective of an optical radiation detected at a sensor after tissue attenuation. The signal quality is examined to determine if it is sufficient to support the use of a full set of wavelengths. If it is determined to be insufficient to support the full set, a reduced number of wavelengths is used.

PRIORITY CLAIM TO RELATED PROVISIONAL APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57. Thepresent application is a continuation of U.S. application Ser. No.15/812,930, filed Nov. 14, 2017, which is a continuation of U.S.application Ser. No. 12/949,271, filed Nov. 18, 2010, which claimspriority to U.S. Provisional Patent Application Ser. Nos. 61/264,182,filed Nov. 24, 2009, and 61/330,253, filed Apr. 30, 2010. The presentapplication incorporates the foregoing disclosures herein by reference.

INCORPORATION BY REFERENCE OF RELATED APPLICATIONS

The present application is related to the following U.S. utilityapplications:

application Filing Ser. No. Date Title Atty Dock. 1 11/367,013 Mar. 1,Multiple Wavelength MLR.002A 2006 Sensor Emitters 2 11/366,955 Mar. 1,Multiple Wavelength MLR.003A 2006 Sensor Equalization 3 11/366,209 Mar.1, Multiple Wavelength MLR.004A 2006 Sensor Substrate 4 11/366,210 Mar.1, Multiple Wavelength MLR.005A 2006 Sensor Interconnect 5 11/366,833Mar. 1, Multiple Wavelength MLR.006A 2006 Sensor Attachment 6 11/366,997Mar. 1, Multiple Wavelength MLR.009A 2006 Sensor Drivers 7 11/367,034Mar. 1, Physiological Parameter MLR.010A 2006 Confidence Measure 811/367,036 Mar. 1, Configurable Physiological MLR.011A 2006 MeasurementSystem 9 11/367,033 Mar. 1, Noninvasive Multi- MLR.012A 2006 ParameterPatient Monitor 10 11/367,014 Mar. 1, Noninvasive Multi- MLR.013A 2006Parameter Patient Monitor 11 11/366,208 Mar. 1, Noninvasive Multi-MLR.014A 2006 Parameter Patient Monitor 12 12/056,179 Mar. 26, MultipleWavelength MLR.015A 2008 Optical Sensor 13 12/082,810 Apr. 14, OpticalSensor Assembly MLR.015A2 2008

The present application incorporates the foregoing disclosures herein byreference.

BACKGROUND

Spectroscopy is a common technique for measuring the concentration oforganic and some inorganic constituents of a solution. The theoreticalbasis of this technique is the Beer-Lambert law, which states that theconcentration c_(i) of an absorbent in solution can be determined by theintensity of light transmitted through the solution, knowing thepathlength d_(λ), the intensity of the incident light I_(0,λ), and theextinction coefficient ε_(i,λ) at a particular wavelength λ. Ingeneralized form, the Beer-Lambert law is expressed as:

$\begin{matrix}{I_{\lambda} = {I_{0,\lambda}e^{{- d_{\lambda}} \cdot \mu_{a,\lambda}}}} & (1) \\{\mu_{a,\lambda} = {\sum\limits_{i = 1}^{n}\; {ɛ_{i,\lambda} \cdot c_{i}}}} & (2)\end{matrix}$

where μ_(a,λ) is the bulk absorption coefficient and represents theprobability of absorption per unit length. The minimum number ofdiscrete wavelengths that are required to solve EQS. 1-2 are the numberof significant absorbers that are present in the solution.

A practical application of this technique is pulse oximetry, whichutilizes a noninvasive sensor to measure oxygen saturation (SpO₂) andpulse rate. In general, the sensor has light emitting diodes (LEDs) thattransmit optical radiation of red and infrared wavelengths into a tissuesite and a detector that responds to the intensity of the opticalradiation after absorption (e.g., by transmission or transreflectance)by pulsatile arterial blood flowing within the tissue site. Based onthis response, a processor determines measurements for SpO₂, pulse rate,and can output representative plethysmographic waveforms. Thus, “pulseoximetry” as used herein encompasses its broad ordinary meaning known toone of skill in the art, which includes at least those noninvasiveprocedures for measuring parameters of circulating blood throughspectroscopy. Moreover, “plethysmograph” as used herein (commonlyreferred to as “photoplethysmograph”), encompasses its broad ordinarymeaning known to one of skill in the art, which includes at least datarepresentative of a change in the absorption of particular wavelengthsof light as a function of the changes in body tissue resulting frompulsing blood. Pulse oximeters capable of reading through motion inducednoise are available from Masimo Corporation (“Masimo”) of Irvine, Calif.Moreover, portable and other oximeters capable of reading through motioninduced noise are disclosed in at least U.S. Pat. Nos. 6,770,028,6,658,276, 6,157,850, 6,002,952 5,769,785, and 5,758,644, which areowned by Masimo and are incorporated by reference herein. Such readingthrough motion oximeters have gained rapid acceptance in a wide varietyof medical applications, including surgical wards, intensive care andneonatal units, general wards, home care, physical training, andvirtually all types of monitoring scenarios.

FIG. 1 illustrates HbO₂ (Oxyhemoglobin) and Hb (Hemoglobin) absorptionμ_(a) versus wavelength. At red and near IR wavelengths below 970 nm,where water has a significant peak, Hb and HbO₂ are the only significantabsorbers normally present in the blood. Thus, typically only twowavelengths are needed to resolve the concentrations of Hb and HbO₂,e.g. a red (RD) wavelength at 660 nm and an infrared (IR) wavelength at940 nm. In particular, SpO₂ is computed based upon a red ratioRed_(AC)/Red_(DC) and an IR ratio IR_(AC)/IR_(DC), which are the ACdetector response magnitude at a particular wavelength normalized by theDC detector response at that wavelength. The normalization by the DCdetector response reduces measurement sensitivity to variations intissue thickness, emitter intensity and detector sensitivity, forexample. The AC detector response is a plethysmograph, as describedabove. Thus, the red and IR ratios can be denoted as NP_(RD) and NP_(IR)respectively, where NP stands for “normalized plethysmograph.” In pulseoximetry, oxygen saturation is calculated from the ratioNP_(RD)/NP_(IR).

SUMMARY OF THE DISCLOSURE

Embodiments of the disclosure are directed to a physiologicalmeasurement system that can automatically adjust the number ofwavelengths used based on a sensor signal that is indicative of theoptical radiation detected at the sensor after tissue attenuation. In anembodiment, the physiological measurement system performs a calibrationprocess upon power up and/or a first attachment to a tissue site. Duringthe calibration process, the system provides test currents to the lightemitting sources in the emitter assembly and examines the sensor signalto determine if the signal quality is sufficient to support the use of afull set of wavelengths. The full set of wavelengths includes eightwavelengths in an embodiment. If it is determined that the signalquality is insufficient to support the full set, a reduced number ofwavelengths is used. In an embodiment, the wavelengths at 660 nm and 905nm, the minimum two wavelengths needed to provide a SpO2 reading, areused in lieu of the full set of wavelengths. In other embodiments, otherreduced numbers of wavelengths are used. In other embodiments, thephysiological measurement system continually monitors signal quality andautomatically adjusts the number of wavelengths used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of oxyhemoglobin and reduced hemoglobin lightabsorption versus wavelength across portions of the red and IR spectrum;

FIG. 2 is a graph of NP ratios versus wavelength illustrating a tissueprofile;

FIG. 3A is a perspective view of a physiological measurement systemutilizing a multiple wavelength sensor;

FIG. 3B is a perspective view of a multiple wavelength sensorembodiment;

FIG. 4A is a general block diagram of a multiple wavelength sensor andsensor controller;

FIG. 4B is a general block diagram of a monitor and a sensor;

FIG. 4C is a general block diagram of an emitter assembly;

FIG. 5A is a general block diagram of an emitter array;

FIG. 5B is a schematic diagram of an emitter array embodiment;

FIGS. 6A-6C are flow diagrams illustrating automatic wavelengthadjustment processes in accordance with various embodiments;

FIG. 7A is a graph of NP ratios versus wavelength illustrating aprobe-off profile;

FIG. 7B is a graph of NP ratios versus wavelength illustrating apenumbra profile;

FIG. 8 is a general block diagram of a confidence measurement system;

FIG. 9A is a graph of normalized plethysmograph (NP) ratios versuswavelength for low and high SpO₂ illustrating a NP envelope;

FIG. 9B is a block diagram of a multiple wavelength probe off detectorutilizing an NP envelope;

FIG. 10A is a graph of NP ratios versus wavelength illustrating a familyof parametric NP curves;

FIG. 10B is a block diagram of a multiple wavelength confidencemeasurement system utilizing parametric NP curves;

FIG. 11A is an NP ratio graph illustrating a family of NP data clusters;

FIG. 11B is a block diagram of a multiple wavelength confidencemeasurement system utilizing NP data clusters; and

FIG. 12 is a graph showing a ratio of normalized detector signal tocurrent provided to an LED.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In this application, reference is made to many blood parameters. Somereferences that have common shorthand designations are referencedthrough such shorthand designations. For example, as used herein, HbCOdesignates carboxyhemoglobin, HbMet designates methemoglobin, and Hbtdesignates total hemoglobin. Other shorthand designations such as COHb,MetHb, and tHb are also common in the art for these same constituents.These constituents are generally reported in terms of a percentage,often referred to as saturation, relative concentration or fractionalsaturation. Total hemoglobin is generally reported as a concentration ing/dL. The use of the particular shorthand designators presented in thisapplication does not restrict the term to any particular manner in whichthe designated constituent is reported.

Embodiments of the disclosure are directed to a physiologicalmeasurement system that can automatically adjust the number ofwavelengths used based on a sensor signal that is indicative of theoptical radiation detected at the sensor after tissue attenuation. Invarious embodiments, the adjustment process utilizes various methods ofNP profile comparison to derive a confidence measurement to measure thequality of the signal detected at the sensor. In other embodiments, thesystem provides test currents to light emitter sources in the emitterassembly and measure sensor signals in response to the light emitted todetermine signal quality. If the signal quality is insufficient tosupport using the full set of wavelengths, the physiological measurementsystem can switch to using less than the full set of wavelengths.

Example Normalized Plethysmograph (NP) Tissue Profile

FIG. 2 illustrates an example of a “tissue profile” 200 for SpO2=97%.For this example, including FIGS. 7A-7B, below, the sensor emits eightwavelengths (610, 620, 630, 655, 700, 720, 800 and 905 nm). The graph isa plot of NP ratios 210 versus wavelength 220, where the NP ratios areof the form NP_(λ1)/NP_(λ2). This is a generalization to multiplewavelengths of the ratio NP_(RD)/NP_(IR) described above in FIG. 1 fortwo (red and IR) wavelengths. In order to provide a common scale forthese NP ratios, the ratios are calculated with respect to a referencewavelength, λr, which may be any of the available wavelengths. Thus, theplotted NP ratios are denoted NP_(λn)/NP_(λr) over the n availablewavelengths, including λr. Note that the NP ratio at the referencewavelength is NP_(λr)/NP_(λr)=1, which is 800 nm in FIG. 2.

As shown in FIG. 2, when a sensor is properly positioned on a tissuesite, the detector only receives LED emitted light that has propagatedthrough the tissue site after tissue scattering and absorption. Thus, atissue profile 200 should reflect the blood constituent absorptioncharacteristics illustrated in FIG. 1, above. For this high oxygensaturation (97%) example, HbO₂ is the only significantly absorbing bloodconstituent and, indeed, the resulting tissue profile 200 is shaped likethe HbO₂ absorption curve 110 (FIG. 1).

FIG. 3A illustrates an example physiological measurement system 300 thatcan output and detect wavelength profiles similar to that shown in FIG.2. In an embodiment, the measurement system 300 includes a monitor 302and a multiple wavelength sensor assembly 310 with enhanced measurementcapabilities as compared with conventional pulse oximetry. Thephysiological measurement system 300 allows the monitoring of a person,including a patient. In particular, the multiple wavelength sensorassembly 310 allows the measurement of blood constituent and relatedparameters in addition to oxygen saturation and pulse rate.Alternatively, the multiple wavelength sensor assembly 310 allows themeasurement of oxygen saturation and pulse rate with increased accuracyor robustness as compared with conventional pulse oximetry.

In an embodiment, the sensor assembly 310 is configured to plug into amonitor sensor port 304. Monitor keys 306 provide control over operatingmodes and alarms, to name a few. A display 308 provides readouts ofmeasured parameters, such as oxygen saturation, pulse rate, HbCO andHbMet to name a few.

FIG. 3B illustrates a multiple wavelength sensor assembly 310 having asensor 330 adapted to attach to a tissue site, a sensor cable 320 and amonitor connector 312. In an embodiment, the sensor 330 is incorporatedinto a reusable finger clip adapted to removably attach to, and transmitlight through, a fingertip. The sensor cable 320 and monitor connector312 are integral to the sensor 330, as shown. In alternativeembodiments, the sensor 330 may be configured separately from the cable320 and connector 312.

FIG. 4A illustrates the sensor 330 having an emitter assembly 332, adetector assembly 334, an interconnect assembly 336 and an attachmentassembly 338. The emitter assembly 332 responds to drive signalsreceived from a sensor controller 340 in the monitor 302 via the cable320 so as to transmit optical radiation having a plurality ofwavelengths into a tissue site. The detector assembly 334 provides asensor signal to the monitor 302 via the cable 320 in response tooptical radiation received after attenuation by the tissue site. Theinterconnect assembly 336 provides electrical communication between thecable 320 and both the emitter assembly 332 and the detector assembly334. The attachment assembly 338 attaches the emitter assembly 332 anddetector assembly 334 to a tissue site, as described above. Additionaldetails of the detector assembly 334, the interconnect assembly 336 andthe attachment assembly 338 are further described in theabove-referenced application. Ser. No. 11/367,013, filed Mar. 1, 2006,entitled “Multiple Wavelength Sensor Emitters,” which has beenincorporated by reference above. The emitter assembly 332 will bedescribed in further details below.

FIG. 4B illustrates a monitor 302 and a corresponding sensor assembly310, as described generally with respect to FIGS. 3A, 3B and 4A above.As discussed above, the sensor assembly 310 houses the emitter assembly332 having emitters. In an embodiment, the emitter assembly 332 isresponsive to drivers within a sensor controller 340 so as to transmitoptical radiation into a tissue site. The sensor 330 also houses adetector assembly 334 that provides a sensor signal 354 responsive tothe optical radiation after tissue attenuation. In an embodiment, thesensor signal 354 is filtered, amplified, sampled and digitized by afront-end 348 and input to a DSP (digital signal processor) 346, whichalso commands the sensor controller 340. The sensor cable 320electrically communicates drive signals from the sensor controller 340to the emitter assembly 332 and a sensor signal 354 from the detectorassembly 334 to a front-end 348. The sensor cable 320 has a monitorconnector 352 that plugs into a monitor sensor port 304.

In an embodiment, the DSP 346 processes the incoming digitalized sensorsignal 354 and determines whether the signal quality requires a changeto the number of wavelengths that are active in the emitter assembly. Inan embodiment, the DSP 346 includes methods and components fordetermining signal quality as shown in FIGS. 8A-12, as will be furtherdescribed below.

In an embodiment, the monitor 302 also has a reader 350 capable ofobtaining information from an information element (IE) 360 in the sensorassembly and transferring that information to the DSP 346, to anotherprocessor or component within the monitor 302, or to an externalcomponent or device that is at least temporarily in communication withthe monitor 302. In an alternative embodiment, the reader function isincorporated within the DSP 346, utilizing one or more of DSP I/O, ADC,DAC features and corresponding processing routines, as examples.Additional details and alternate embodiments for components shown inFIG. 4B are further described in FIGS. 41-46 of the above-referencedapplication. Ser. No. 11/367,013, filed Mar. 1, 2006, entitled “MultipleWavelength Sensor Emitters.”

In an embodiment, the monitor connector 352 houses the informationelement 360, which may be a memory device or other active or passiveelectrical component. In a particular embodiment, the informationelement 360 is an EPROM, or other programmable memory, or an EEPROM, orother reprogrammable memory, or both. In an alternative embodiment, theinformation element 360 is housed within the sensor 330, or aninformation element 360 is housed within both the monitor connector 352and the sensor 330. In yet another embodiment, the emitter assembly 332has an information element 360, which is read in response to one or moredrive signals from the sensor controller 340. In a further embodiment, amemory information element is incorporated into the emitter array 400(FIG. 5A) and has characterization information relating to the LEDs 490(FIG. 5B). In one advantageous embodiment, trend data relating to slowlyvarying parameters, such as perfusion index, HbCO or METHb, to name afew, are stored in an IE memory device, such as EEPROM.

Emitter Assembly

FIG. 4C illustrates an emitter assembly 332 having an emitter array 372,a substrate 370 and equalization 374. The emitter array 372 has multiplelight emitting sources, each activated by addressing at least one rowand at least one column of an electrical grid. The light emittingsources are capable of transmitting optical radiation having multiplewavelengths. The equalization 374 accounts for differences in tissueattenuation of the optical radiation across the multiple wavelengths soas to at least reduce wavelength-dependent variations in detectedintensity. The substrate 370 provides a physical mount for the emitterarray and emitter-related equalization and a connection between theemitter array and the interconnection assembly. Advantageously, thesubstrate 370 also provides a bulk temperature measurement so as tocalculate the operating wavelengths for the light emitting sources. Theequalization 374 and the substrate 370 are described in further detailin above-referenced application. Ser. No. 11/367,013, filed Mar. 1,2006, entitled “Multiple Wavelength Sensor Emitters,” which has beenincorporated by reference above.

Emitter Array

FIG. 5A illustrates an emitter array 400 having multiple light emitters(LE) 410 capable of emitting light 402 having multiple wavelengths intoa tissue site 1. The emitter array 400 emits optical radiation havingmultiple wavelengths of predetermined nominal values, advantageouslyallowing multiple parameter measurements. In particular, the emitterarray 400 has multiple light emitting diodes (LEDs) 410 that arephysically arranged and electrically connected in an electrical grid tofacilitate drive control, equalization, and minimization of opticalpathlength differences at particular wavelengths. In an embodiment, anoptical filter is advantageously configured to provide intensityequalization across a specific LED subset. The substrate 370 isconfigured to provide a bulk temperature of the emitter array 400 so asto better determine LED operating wavelengths.

As shown in FIG. 5A, row drivers 376 and column drivers 378 areelectrically connected to the light emitters 410 and activate one ormore light emitters 410 by addressing at least one row 420 and at leastone column 440 of an electrical grid. In an embodiment, the lightemitters 410 each include a first contact 412 and a second contact 414.The first contact 412 of a first subset 430 of light emitters is incommunication with a first conductor 420 of the electrical grid. Thesecond contact 414 of a second subset 450 of light emitters is incommunication with a second conductor 440. In an embodiment, each subsetcomprises at least two light emitters, and at least one of the lightemitters of the first and second subsets 430, 450 are not in common. Adetector 334 is capable of detecting the emitted light 402 andoutputting a sensor signal responsive to the emitted light 402 afterattenuation by the tissue site 1 via monitor connector 352. As such, thesensor signal is indicative of at least one physiological parametercorresponding to the tissue site 1, as described above.

FIG. 5B illustrates an emitter array 400 having LEDs 490 connectedwithin an electrical grid of n rows and m columns totaling n+m drivelines 488, 486, where n and m integers greater than one. The electricalgrid advantageously minimizes the number of drive lines required toactivate the LEDs 490 while preserving flexibility to selectivelyactivate individual LEDs 490 in any sequence and multiple LEDs 490simultaneously. The electrical grid also facilitates setting LEDcurrents so as to control intensity at each wavelength, determiningoperating wavelengths and monitoring total grid current so as to limitpower dissipation. The emitter array 400 is also physically configuredin rows 480. This physical organization facilitates clustering LEDs 490according to wavelength so as to minimize pathlength variations andfacilitates equalization of LED intensities.

As shown in FIG. 5B, one embodiment of an emitter array 400 comprises upto sixteen LEDs 490 configured in an electrical grid of four rows 480and four columns 482. Each of the four row drive lines 488 provide acommon anode connection to four LEDs 490, and each of the four columndrive lines 486 provide a common cathode connection to four LEDs 490.Thus, the sixteen LEDs 490 are advantageously driven with only eightwires, including the four anode drive lines and the four cathode drivelines as shown. This compares favorably to conventional common anode orcathode LED configurations, which require more drive lines. In aparticular embodiment, the emitter array 400 is partially populated witheight LEDs having nominal wavelengths as shown in TABLE 1. Further, LEDshaving wavelengths in the range of 610-630 nm are grouped together inthe same row. The emitter array 400 is adapted to a physiologicalmeasurement system 300 (FIG. 3A) for measuring H_(b)CO and/or METHb inaddition to S_(p)O₂ and pulse rate.

TABLE 1 Nominal LED Wavelengths LED λ Row Col D1 630 1 1 D2 620 1 2 D3610 1 3 D4 1 4 D5 700 2 1 D6 730 2 2 D7 660 2 3 D8 805 2 4 D9 3 1 D10 32 D11 3 3 D12 905 3 4 D13 4 1 D14 4 2 D15 4 3 D16 4 4

Also shown in FIG. 5B, row drivers 376 and column drivers 484 located inthe monitor 302 selectively activate the LEDs 490. In particular, rowand column drivers 376, 484 function together as switches to Vcc andcurrent sinks, respectively, to activate LEDs and as switches to groundand Vcc, respectively, to deactivate LEDs. This push-pull driveconfiguration advantageously prevents parasitic current flow indeactivated LEDs. In a particular embodiment, only one row drive line488 is switched to Vcc at a time. One to four column drive lines 486,however, can be simultaneously switched to a current sink so as tosimultaneously activate multiple LEDs within a particular row. LEDdrivers and the process of facilitating intensity equalization throughthe activation of two or more LEDs of the same wavelength are furtherdescribed in the above-referenced application. Ser. No. 11/367,013,filed Mar. 1, 2006, entitled “Multiple Wavelength Sensor Emitters.”

Although an emitter assembly is described above with respect to an arrayof light emitters each configured to transmit optical radiation centeredaround a nominal wavelength, in another embodiment, an emitter assemblyadvantageously utilizes one or more tunable broadband light sources,including the use of filters to select the wavelength, so as to minimizewavelength-dependent pathlength differences from emitter to detector. Inyet another emitter assembly embodiment, optical radiation from multipleemitters each configured to transmit optical radiation centered around anominal wavelength is funneled to a tissue site point so as to minimizewavelength-dependent pathlength differences. This funneling may beaccomplished with fiberoptics or mirrors, for example. In furtherembodiments, the LEDs 490 can be configured with alternativeorientations with correspondingly different drivers among various otherconfigurations of LEDs, drivers and interconnecting conductors.

Automatic Wavelength Adjustment Processes

FIGS. 6A-6C are flow diagrams that illustrate the automatic wavelengthadjustment processes in accordance with various embodiments. FIG. 6Aillustrates an automatic wavelength adjustment process 500. In anembodiment, the process 500 is executed as part of or during acalibration process that is executed when the physiological measurementsystem 300 is first powered up and/or when the sensor assembly 310 isattached or re-attached to a tissue site. In another embodiment, theprocess 500 is executed periodically when the physiological measurementsystem 300 is in use.

As shown, the process 500 begins in an embodiment at block 502 with thedetector 334 receiving a signal after tissue attenuation as describedwith respect to FIG. 4A. At block 504, the received signal is processedto determine signal quality. In an embodiment, the DSP 346 is configuredto process the received signal that has been digitalized by thefront-end 348 to determine signal quality. At block 506, the signalquality is evaluated to determine if it is sufficient to support a fullset of active wavelengths. In an embodiment, the full set of activewavelengths includes the eight wavelengths as set forth in TABLE 1above.

If the signal quality is determined to be lower than that which isneeded to support the full set of active wavelengths, at block 510 thephysiological measurement system 300 will use less than the full set ofactive wavelengths. In an embodiment, the DSP 346 sends a signal to thesensor controller 340 (FIG. 4B) to effectuate the use of less than thefull set of active wavelengths. In an embodiment, the two activewavelengths used are at 660 nm (Red) and 905 nm (IR), the minimum twoneeded to detect SpO2. With reference to TABLE 1 and FIG. 5B, forexample, LEDs D7 and D12 would be activated at block 510 while the restof LEDs remain inactive.

In the alternative, if the signal quality is deemed to be sufficient tosupport the full set of active wavelengths, then at block 508 thephysiological measurement system 300 will use the full set of activewavelengths. In an embodiment, the full set of active wavelengthsincludes the eight shown in TABLE 1. For example, the corresponding LEDsshown in TABLE 1 would be activated at block 508. In an embodiment, theprocess 500 then begins again at block 502. Various methods ofdetermining and evaluating signal quality, including criteria fordetermining sufficiency of a signal quality to support a full set ofactive wavelengths, will be further described with respect to FIGS.8A-12.

FIG. 6B shows another process 520 for automatic wavelength adjustment inwhich the physiological measurement system 300 periodically determineswhether the full set of wavelengths should be used. The process 520begins in an embodiment at block 522 with the detector 334 receiving asignal after tissue attenuation as described with respect to FIG. 4A. Atblock 524, the received signal is processed to determine signal quality.In an embodiment, the DSP 346 is configured to process the receivedsignal that has been digitalized by the front-end 348 to determinesignal quality. At block 526, the signal quality is evaluated todetermine whether it is sufficient to support a full set of activewavelengths. In an embodiment, the full set of active wavelengthsincludes the eight wavelengths as set forth in TABLE 1 above.

If the signal quality is deemed to be lower than that which is needed tosupport the full set of active wavelengths, then at block 530 thephysiological measurement system 300 will use less than the full set ofactive wavelengths. The DSP 346 can send a change signal to the sensorcontroller 340 (FIG. 4B) if the physiological measurement system 300 iscurrently using the full set of active wavelengths. For example, thechange may reduce the number of active wavelengths from the eight shownin TABLE 1 to two (e.g., 660 nm (Red) and 905 nm (IR)). However, if thephysiological measurement system 300 is already using less than the fullset of active wavelengths, no action is performed at block 530. Ineither case, the process 520 returns to block 522 where a new signalwill be received and processed at the next sampling cycle.

In the alternative, if the signal quality is deemed to be sufficient tosupport the full set of active wavelengths, then at block 528 thephysiological measurement system 300 will either continue using the fullset of active wavelengths (if the full set is already used) or change tousing the full set of active wavelengths (if less than the full set isbeing used). If a change is needed, in an embodiment the DSP 346 cansend a change signal to the sensor controller 340. The process 520 thenreturns to block 522, where a new signal will be received and processedat the next sampling cycle.

FIG. 6C shows another process 540 for automatic wavelength adjustment inwhich the physiological measurement system 300 periodically adjusts thenumber of wavelengths used depending on the detected signal quality. Theprocess 540 begins in an embodiment at block 542 with the detector 334receiving a signal after tissue attenuation as described with respect toFIG. 4A. At block 544, the received signal is processed to determinesignal quality. In an embodiment, the DSP 346 is configured to processthe received signal that has been digitalized by the front-end 348 todetermine signal quality. At block 546, the signal quality is evaluatedto determine whether it is sufficient to support additional activewavelengths. If so, then at block 548 the physiological measurementsystem 300 will use additional active wavelengths (if less than the fullset is being used). If a change is needed, in an embodiment the DSP 346can send a change signal to the sensor controller 340. The process 540then returns to block 542, where a new signal will be received andprocessed at the next sampling cycle.

If the signal quality is deemed to not be sufficient to support moreactive wavelengths than those that are currently being used, then atblock 550 the physiological measurement system 300 will determinewhether the signal qualify can at least support the current set ofactive wavelengths. If it is sufficient, no action is taken at block 552and the current number of active wavelengths will continue to be used.Otherwise, the physiological measurement system 300 will use fewerwavelengths. The DSP 346 can send a change signal to the sensorcontroller 340 (FIG. 4B). In any case, the process 540 returns to block542 where a new signal will be received and processed at the nextsampling cycle.

In various embodiments, portions of processes described in FIGS. 6A-6Ccan be performed at the front-end 348, the sensor controller 340, theDSP 346 or any other component within physiological measurement system300.

Signal Quality Determination

FIGS. 7A-7B illustrate profiles of two conditions that are indicative ofdegraded signal quality. FIGS. 8A-11B describe example methods ofderiving a confidence measurement that can be used to measure signalquality, and in particular, to detect degraded signal quality shown inthe examples illustrated below.

FIG. 7A illustrates an example of a probe-off profile 700. When a sensoris completely dislodged from a patient, a so-called “probe off”condition occurs. Despite a probe off condition, an optical sensor maycontinue to detect an AC signal, which can be induced at the detector byother than pulsatile arterial absorption of LED emitted light. Forexample, small patient movements, vibrations, air flow or otherperturbations may cause the pathlength between the LEDs and the detectorto vary, resulting in an AC detector signal that can be mistakenlyinterpreted by the monitor as due to pulsatile arterial blood. Further,ambient light may reach the detector, and any modulation of the ambientlight due to AC power, power fluctuations, moving objects, such as afan, among other perturbations can be also mistaken as a pulsatilearterial signal. Probe off errors are serious because a bloodconstituent monitor may display normal results, such as oxygensaturation, when, in fact, the sensor is not properly attached to thepatient, potentially leading to missed severe desaturation events. Asshown in FIG. 7A, a probe-off profile 700 is readily apparent as it doesnot have a shape related to the absorption characteristics of hemoglobinconstituents.

FIG. 7B illustrates an example of a penumbra profile 702. When a sensoris not properly positioned or becomes partially dislodged, a penumbracondition may occur, where the detector is “shadowed” by a tissue site,such as a finger, but also receives some light directly from theemitters or indirectly reflected off the sensor housing, or both. As aresult, the DC signal at the detector rises significantly, which lowersthe AC/DC ratio (NP). Because red wavelengths are more significantlyabsorbed by Hb and HbO2, the penumbra condition is most noticeable atthe red portion 704 of the NP_(An)/NP_(Ar). This effect is readily seenin the penumbra profile 702 as compared to a normal tissue profile 200(FIG. 2).

Advantageously, a physiological parameter confidence measurement system,as described below, can distinguish a tissue profile 200 (FIG. 2) from aprobe-off profile 700 (FIG. 7A) or penumbra profile 702 (FIG. 7B), asexamples. Further, a physiological parameter confidence measurementsystem can provide indications that the detector signal is degraded asthe result of various physiological and non-physiological phenomenons.

Physiological Parameter Confidence Measurement System

FIG. 8 illustrates a physiological parameter confidence measurementsystem 800 having a physiological data 808 input, a confidence indicator824 output and a probe-off indicator 826 output. In an embodiment,physiological data 808, such as the NP ratios described above, isderived from a sensor 802 generating a sensor signal 804 responsive tomultiple wavelengths of optical radiation transmitted into andattenuated by a tissue site. The confidence indicator 824 provides anobserver with some measure of “goodness” for the physiological data 808.That is, if confidence is high, it is likely the physiological data 816is representative of a physiological condition or state. If confidenceis low, the physiological data 808 may be less representative of aphysiological condition or state. If the confidence is very low, aprobe-off indicator 826 may be generated to alert an observer to thepossibility that a sensor from which the physiological data 808 isderived is not properly positioned on a tissue site and may not begenerating physiologically significant data. In an embodiment, aconfidence measure may be provided as a percentage, such as 0-100%.

The confidence measure can be used to measure signal quality in theprocesses described above with respect to FIGS. 6A-6C. For example, theconfidence level threshold may be set at 80% in order for a full set ofwavelengths to be used. In other embodiments, the threshold may be setby the user of the physiological measurement system 300. In variousembodiments, a confidence indicator 824 corresponding to a confidencemeasure may be visual (through a display 822) or audible (through analarm 828) or both. The visual or audible indication may assist the userin setting the threshold.

As shown in FIG. 8, the physiological parameter confidence measurementsystem 800 also has a parameter estimator 810, a physiological datareference 814 and a confidence measurer 818. The parameter estimator 810derives one or more physiological parameter estimates, {circumflex over(P)}, 812 based upon the physiological data 810. The parameter estimateor estimates 812 are used to select one or more data clusters 816 fromthe physiological data reference 814. In an embodiment, thephysiological data reference 814 is a collection of predeterminedphysiological data organized in data clusters. For example thephysiological data reference 814 may contain clinically-derivedphysiological data organized according to corresponding values of aphysiological parameter determined by a “gold standard” instrument. In aparticular embodiment, the physiological data are NP ratios obtained forvarious physiological parameters, such as SpO₂, HbCO, HbMet, Hbt,fractional oxygen saturation, bilirubin or glucose to name a few, asmeasured with a standardized cooximeter, for example. In an embodiment,the physiological data reference 814 is a non-volatile memory or otherdata storage device containing predetermined physiological data. Theconfidence measurer 818 uses the physiological data 808 and the selecteddata cluster or data clusters 816 to generate the confidence indicator824, the probe-off indicator 826 or both.

A confidence measurement and confidence indicator, as described herein,may be combined with other signal quality and data confidencemeasurements and indicators, such as those described in U.S. Pat. No.6,996,427 titled Pulse Oximetry Data Confidence Indicator and U.S. Pat.No. 6,606,511 titled Pulse Oximetry Pulse Indicator, both patentsassigned to Masimo Corporation, Irvine, Calif. and incorporated byreference herein. A probe off measurement and probe off indicator asdescribed herein may be combined with other probe off measurements andindicators, such as those described in U.S. Pat. No. 6,654,624 titledPulse Oximeter Probe-Off Detector and U.S. Pat. No. 6,771,994 titledPulse Oximeter Probe-Off Detection System, both patents assigned toMasimo Corporation, Irvine, Calif. and incorporated by reference herein.

FIG. 9A illustrates NP ratio versus wavelength curves computed from amultiple wavelength sensor, such as described in the U.S. patentapplication titled “Multiple Wavelength Sensor,” referenced above. Inthis example, the sensor emits eight wavelengths (620, 630, 660, 700,730, 805, 905 and 960 nm). As with FIGS. 8A and 8B, the confidencemeasurement derived from the embodiments shown in FIGS. 9A and 9B can beused to adjust the number of active wavelengths that is used by thephysiological measurement system 300.

Shown in FIG. 9A is a low oxygen saturation curve 610, e.g. SpO₂=70% anda high oxygen saturation curve 620, e.g. SpO₂≈100%. By comparison, aconventional two wavelength pulse oximetry sensor, as described above,results in a single point on a particular curve. Advantageously, the NPratio curves 910, 920 represent a tissue profile that can be compared toa particular sensor response to determine if a physiologicallysignificant measurement has been made. In an embodiment, the NP ratiocurves 910, 920 delineate the boundaries of a physiologicallysignificant NP ratio region 930. Although described above with respectto SpO₂, such regions or boundaries can be derived for otherphysiological parameters such as HbCO, HbMet, Hbt, fractional oxygensaturation, bilirubin or glucose to name a few.

FIG. 9B illustrates one embodiment of a physiological parameterconfidence measurement system 950 utilizing a NP ratio region such asdescribed with respect to FIG. 9A, above. The confidence measurementsystem 950 has input NP ratios 952 measured in response to a multiplewavelength sensor, reference NP ratio region 956 that delineatesphysiologically significant NP ratios 930 (FIG. 9A), and a comparator954. In one particular embodiment, the NP ratio region 956 ispredetermined from clinically-derived data for one or more parameters ofinterest, such as SpO₂, HbCO, HbMet, Hbt, fractional oxygen saturation,bilirubin or glucose, to name a few. In another particular embodiment,the NP ratio region 956 is theoretically calculated. The comparator 954compares the input NP ratios 952 with the NP ratio region 956 andgenerates a probe-off indicator 958 if any, or more than a predeterminenumber, of the input NP ratios 952 fall outside of an NP ratio region956.

FIG. 10A illustrates a family of parametric NP ratio versus wavelengthcurves 1000 computed from a multiple wavelength sensor, such asreferenced above. Each curve represents a different value of a measuredparameter, such as SpO₂. For example, there may be a curve for each ofSpO₂=70%, 75%, 80%, . . . 100%. Advantageously, such curves moreprecisely indicate physiologically significant multiple wavelengthsensor measurements as compared to a bounded NP ratio region 930 (FIG.9A) such as described with respect to FIGS. 9A-9B, above. The confidencemeasurement derived by the method shown in FIGS. 10A-10B can be used toadjust the number of active wavelengths that is used by thephysiological measurement system 300.

FIG. 10B illustrates another embodiment of a physiological parameterconfidence measurement system 1008 utilizing parametric NP ratio curves,such as described with respect to FIG. 10A, above. The confidencemeasurement system 1008 has input NP ratios 1010 measured in response toa multiple wavelength sensor, a parameter estimator 1012, referenceparametric curves 1016 and a difference calculator 1020. The parameterestimator 1012 inputs the NP ratios 1010 so as to generate a parameterestimate 1014, such as SpO₂, HbCO, HbMet, Hbt, fractional oxygensaturation, bilirubin or glucose, to name a few. The estimated parameter1014 selects one or more of the reference parametric curves 1016, whichare predetermined from clinically-derived data that is stored in memoryor data that is mathematically pre-calculated or calculated in real timeand stored in memory. The difference calculator 1020 measures thedifference between the NP ratios 1010 and the selected parametric curve1016. For example, a mean-squared error calculation can be made betweenthe input NP ratios 1010 and the selected parametric curve 1018. Theresulting difference calculation is used as a confidence measure ortranslated into a confidence measure and a confidence indicator output1022 is generated accordingly. Alternatively, or in addition to aconfidence measure, a probe off condition can be indicated if thedifference calculation is larger than a predetermined value or theconfidence measure is less than a predetermined value. In anotherembodiment, a correlation calculator is used in place of the differencecalculation. The confidence measurement derived from the embodimentsshown in FIGS. 10A-10B can also be used to adjust the number of activewavelengths that is used by the physiological measurement system 300.

FIG. 11A illustrates a family of data clusters 1100 shown in twodimensions by way of example. Each data cluster 1100 represents NPratios clinically measured across a population for specific values 1104of a selected parameter P, such as P₁, P₂, P₃ and P₄ as shown. Each datacluster 1100 defines a region 1102 of NP ratios measured for aparticular parameter value 1104 and has a probability distribution, suchas a normal distribution, over the indicated region 1102.

For example, the clinical data can be organized as a table of knownvalues of P, corresponding NP ratios measured over a population, and therelative number of occurrences of particular NP ratio values for eachvalue of P. The relative number of occurrences of particular NP ratiovalues for a particular value of P yields an NP ratio probabilitydistribution for that value of P. Thus, each P value 1104 in the tablehas a corresponding data cluster 1100 of measured NP ratios and anassociated probability distribution for those NP ratios.

FIG. 11B illustrates yet another embodiment of a physiological parameterconfidence measurement system 1120 utilizing NP data clusters andcorresponding probability distributions, such as described with respectto FIG. 11A, above. The confidence measurement system 1120 has input NPratios 1122 measured in response to a multiple wavelength sensor, aparameter estimator 1124, reference data clusters 1128 and a probabilitycalculator 1132. The parameter estimator 1124 inputs the NP ratios 1122so as to generate a parameter estimate 1126, such as described withrespect to other embodiments, above. In an embodiment, the referencedata clusters 1128, such as described with respect to FIG. 11A, arestored in a memory device, such as an EPROM. The estimated parameter1130 is compared with the reference data clusters 1140 so as todetermine the closest region 1102 (FIG. 11A) or closest overlappingportion of two regions 1102 (FIG. 11A). The probability calculator 1132computes a probability based upon the distribution above the selectedregion 1102 (FIG. 11A). A confidence measure is also derived based uponthe calculated probability. In a particular embodiment, the confidencemeasure is the calculated probability. A confidence indicator 1134 isgenerated in response to the confidence measure. In an embodiment, ifthe confidence probability or the calculated confidence measure is belowa predetermined threshold, a probe-off indicator 1136 is generated. Inparticular embodiments, the confidence indicator 1134 or probe-offindicator 1136 or both may be alphanumeric or digital displays, opticalindicators or alarms or similar audible indicators, to name a few. Theconfidence measurement derived from the embodiments shown in FIGS.11A-11B can also be used to adjust the number of active wavelengths thatis used by the physiological measurement system 300.

Automatic Wavelength Adjustment During Calibration

Besides utilizing the confidence measurements derived from the methodsand systems shown in FIGS. 8A-11B for automatic wavelength adjustment,embodiments of the physiological measurement system 300 can alsoautomatically adjust the number of active wavelengths based on theresults of a calibration process.

FIG. 12 shows a graph 1200 illustrating a signal calibration processperformed by the physiological measurement system 300. The graph plotsthe Analog-to-Digital Conversion (ADC) signal output (i.e. thedigitalized sensor signal) against the current supplied to an LED in theemitter assembly 332. The ADC output may be from the front-end 348 shownin FIG. 4A, for example. As shown, the ADC signal output ranges from 0to 1 on a normalized scale. In an embodiment, an ideal range of outputis preferably between 0.05 to 0.80, with an ideal operational output atabout 0.2. The ideal range of output provides a proper determination ofphysiological data measurements.

In an embodiment, the physiological measurement system 300 performscalibration by sending a small test current through each of the LEDsthat is used in emitting optical radiation at the full set of activewavelengths (e.g. the LEDs shown in TABLE 1). The system can, forexample, send a 5 milliamp current, as denoted by the symbol I₁ in graph1200. The detector then records the detected signal after tissueattenuation. A sample input-output is shown in line 1204, whichillustrates the ratio of measured, digitalized sensor signal to theinput current provided to the LED. The calibration can then send anadditional, larger test current through the LED, e.g. 10 milliamps, asdenoted by the symbol I₂. Based on the level of the measured sensorsignal(s) in response to the one or more test currents provided to theLED, the physiological measurement system 300 can determine whether asensor signal output in the acceptable range can be obtained when alarger operational current is applied. For example, the physiologicalmeasurement system 300 can use the measured outputs from the testcurrents to extrapolate a likely sensor signal output 1202 (shown inFIG. 12 as having a normalized ADC of 0.2) based on an anticipatedoperational current I_(oper). In an embodiment, the DSP 346 performsthese determination calculations. In other embodiments, they areperformed by other components such as the front end 348.

In an embodiment, the calibration performs the same or similar test foreach of the LEDs that is used in emitting optical radiation at the fullset of active wavelengths, and determines whether the extrapolatedsignal output for the LED(s) for each individual wavelength isacceptable. In the example configuration shown in TABLE 1, where thereis a one-to-one correspondence between LEDs and wavelengths, thecalibration process would determine whether the extrapolated signaloutput for each LED is within the acceptable range. In an embodiment,the extrapolation takes into account that while each active LED may bedriven by a different amount of operational current, an overall gain isapplied to all active LEDs in the emitter array. Therefore, in anembodiment, the calibration process also attempts to determine anoperational current for each active LED in order to have all sensorsignals fall within the acceptable ADC range, as illustrated in theexample in FIG. 12.

In an embodiment, if one or more extrapolated signal outputs for aparticular wavelength are not in the acceptable range, the physiologicalmeasurement system 300 uses a fewer number of active wavelengths, i.e.,the associated LED(s), than the full set of active wavelengths. Forexample, in an embodiment where the full set of active wavelengthscomprises eight wavelengths, if any of the eight wavelengths returns anunacceptable result in calibration, the reduction can go from eightactive wavelengths to two. The two can be of the wavelengths 660 nm(red) and 905 nm (IR), the two needed for providing a SpO2 reading. Inan embodiment, the LED(s) for the two active wavelengths are activatedat a longer duty cycle (½ cycle/wavelength) than when the full set ofactive wavelengths is used (⅛ cycle/wavelength).

In other embodiments, the number of active wavelength is first reducedfrom eight to four, and then from four to two. In embodiments in whichthe physiological measurement system includes twelve active wavelengths,the number can be progressively reduced from twelve to eight to four totwo, if the calibration results necessitate such a reduction. In otherembodiments, the physiological measurement system 300 does not follow apre-set reduction routine but instead attempts to maximize the number ofphysiological data measurements that can be obtained given the number ofwavelengths that pass the calibration test. Thus, for example, insteadof reducing from twelve to two when one wavelength fails the calibrationtest, the physiological measurement system 300 can reduce to ten, if theremaining ten can all be used to determine physiological datameasurements.

Additional Embodiments

In an embodiment, the physiological measurement system 300 may return atleast one physiological data measurement even when the detected signaldoes not support a full set of physiological data measurements. Forexample, if the detected signal indicates that a patient's perfusion istoo low to support an Hb measurement but can otherwise support a SpO2measurement, the physiological measurement system 300 may return theSpO2 measurement.

In an embodiment, the patient's perfusion level is used in theafore-mentioned confidence calculations. In an embodiment, the observedperfusion index is used as a factor in determining confidence. Inanother embodiment, the confidence level is determined based onperfusion alone. For example, an observed perfusion index that isoutside of an acceptable range (e.g. below a threshold) would lead to alow confidence level.

In an embodiment, the physiological measurement system 300 provides useroptions for configuring the use of less than a full set of wavelengths.The options allow a user to configure the physiological measurementsystem 300 to specify the manner in which the number of wavelengths arereduced based on user-specified or pre-specified confidence level(s).For example, a user can configure the physiological measurement system300 to use two wavelengths if the confidence level drops below a certainuser-specified or pre-specified level. In another embodiment, a user canconfigure a confidence level below which a particular physiological datameasurement is not returned by the physiological measurement system 300.

A multiple wavelength sensor with automatic wavelength adjustment hasbeen disclosed in detail in connection with various embodiments. Theseembodiments are disclosed by way of examples only and are not to limitthe scope of the claims that follow. One of ordinary skill in art willappreciate many variations and modifications.

1-28. (canceled)
 29. An optical non-invasive physiological parametermeasurement system comprising: one or more light emitting sourcesconfigured to emit light at a plurality of wavelengths; a sensorconfigured to detect light emitted by the one or more light emittingsources after the emitted light is attenuated by body tissue, and togenerate an output signal useable to measure at least one physiologicalparameter of the body tissue; and a processor configured to: cause theone or more light emitting sources to emit light at a first set of theplurality of wavelengths; determine a confidence measurement value basedon a first output signal received from the sensor based on detectedlight emitted at the first set of the plurality of wavelengths; causethe one or more light emitting sources to emit light at a second set ofthe plurality of wavelengths by deactivating at least one of theplurality of wavelength emissions when the confidence measurement valueis less than a threshold value; and determine a physiological parametermeasurement based on a second output signal received from the sensorbased on detected light emitted at less than all of the plurality ofwavelengths.
 30. The system of claim 29, wherein the confidencemeasurement is further determined based on a physiological datareference.
 31. The system of claim 30, wherein the physiological datareference comprises a normalized plethysmograph ratio region bounded bya high normalized plethysmograph ratio curve and a low normalizedplethysmograph ratio curve.
 32. The system of claim 31, wherein the highnormalized plethysmograph ratio curve is a high oxygen saturation (SpO₂)curve and the low normalized plethysmograph ratio curve is a low oxygensaturation (SpO₂) curve.
 33. The system of claim 30, wherein thephysiological data reference comprises a reference parametric curve thatis predetermined from clinically-derived data.
 34. The system of claim30, wherein the physiological data reference comprises a data clusterdefining a region of normalized plethysmograph values.
 35. The system ofclaim 30, wherein the second set of the plurality of wavelengthscomprises two wavelengths.
 36. The system of claim 35, wherein one ofthe two wavelengths is in the red range and the other of the twowavelengths is in the infrared range.
 37. The system of claim 29,wherein the plurality of wavelengths comprises at least eightwavelengths.
 38. The system of claim 29, wherein the physiologicalparameter measurement comprises a SpO₂, HbCO, HbMet, Hbt, factionaloxygen saturation, bilirubin, or glucose measurement.
 39. A method forautomatically adjusting a number of a plurality of wavelengths used in aphysiological measurement system, the method comprising: emitting lightat a first set of a plurality of wavelengths with one or more lightemitting sources; detecting, with a sensor, light emitted by one or morelight emitting sources after attenuation by body tissue, the sensorgenerating a first output signal; determining a confidence measurementvalue based on a first output signal received from the sensor based onthe detected light emitted at the first set of the plurality ofwavelengths; deactivating at least one of the plurality of wavelengthemissions when the confidence measurement value is less than a thresholdvalue to cause the plurality of light emitting sources to emit light ata second set of the plurality of wavelengths; and determining aphysiological parameter measurement based on a second output signalreceived from the sensor based on the detected light emitted at thesecond set of the plurality of wavelengths.
 40. The method of claim 39,wherein determining the confidence measurement value is further based ona physiological data reference.
 41. The method of claim 40, wherein thephysiological data reference comprises a normalized plethysmograph ratioregion bounded by a high normalized plethysmograph ratio curve and a lownormalized plethysmograph ratio curve.
 42. The method of claim 41,wherein the high normalized plethysmograph ratio curve is a high oxygensaturation (SpO₂) curve and the low normalized plethysmograph ratiocurve is a low oxygen saturation (SpO₂) curve.
 43. The method of claim40, wherein the physiological data reference comprises a referenceparametric curve that is predetermined from clinically-derived data. 44.The method of claim 40, wherein the physiological data referencecomprises a data cluster defining a region of normalized plethysmographvalues.
 45. The method of claim 40, wherein the second set of theplurality of wavelengths comprises two wavelengths.
 46. The method ofclaim 45, wherein one of the two wavelengths is in the red range and theother of the two wavelengths is in the infrared range.
 47. The method ofclaim 39, wherein the plurality of wavelengths comprises at least eightwavelengths.
 48. The method of claim 39, wherein the physiologicalparameter measurement comprises a SpO₂, HbCO, HbMet, Hbt, factionaloxygen saturation, bilirubin, or glucose measurement.